United Nations secretary-general Ban Ki-moon says he believes a chemical weapons report will confirm that poison gas was used in Syria.

AFP: Spencer Platt

United Nations secretary-general Ban Ki-moon says he believes chemical weapons experts will confirm that poison gas was used in the massacre in Damascus last month which killed more than 1,400 people, including hundreds of children.

In apparently candid comments made during a meeting at the UN headquarters, Mr Ban did not say whether Bashar al-Assad's forces were responsible for the August 21 attack, but did say Syria's president has committed many crimes against humanity.

"I believe that the report will be an overwhelming report that chemical weapons (were) used, even though I cannot publicly say at this time before I receive this report," he said.

His remark that he could not make his thoughts public has raised doubts about whether he knew the comments were being broadcast.

Key points:

Ban believes UN report will prove chemical weapons were used

Ban accuses Assad of crimes against humanity

Ban does not attribute blame for Aug 21 attack to Assad's regime

UN members expect the report to be released on Monday

Russia and US locked in discussions on how to bring Syria's weapons under foreign control

Russia pushing for 'Geneva 2' in a bid to initiate peace talks

US, France and UK to meet on Monday

Mr Ban also said Mr Assad must face "accountability" as part of any political solution to end the conflict.

"What happened is that he has committed many crimes against humanity," he said.

"Therefore, I'm sure that there will be surely the process of accountability when everything is over."

UN inspection team leader Ake Sellstrom is due to travel to New York this weekend to deliver the report and brief Mr Ban on the findings.

France's UN ambassador, Gerard Araud, says Monday is the tentative date for the report to be presented to the Security Council and other UN member states.

While Mr Sellstrom's report will not explicitly pin the blame on either side, diplomats say the facts they gathered could suggest which side was responsible.

The United States and other Western powers blame forces loyal to Mr Assad for the attack, while Russian president Vladimir Putin asserts there is "every reason to believe" it was carried out by rebels.

US and Russian discussions on Syria continue

Talks between US secretary of state John Kerry and Russia's foreign minister Sergei Lavrov will continue in Geneva as they search for an agreement on how to enforce a plan to divest Syria of its chemical weapons.

Mr Assad vowed yesterday to place Syria's chemical weapons under foreign control, in line with Moscow's proposal.

I believe that the report will be an overwhelming, overwhelming report that chemical weapons (were) used, even though I cannot publicly say at this time before I receive this report.

UN Secretary-General Ban Ki-moon

"We are staying, probably, they will finalise it through the night," a spokeswoman for Mr Lavrov said.

"I am not sure about tomorrow (Saturday), but they will go through the night.

"It is a sign that we are going on, that we proceed with talking and negotiating.

"Now it is like a real negotiating process, they are working on some real substance."

The plan from Moscow was an 11th hour proposal that led US president Barack Obama to put off threatened US military action against the Syrian regime.

Washington wants to see if Mr Assad is serious about putting his chemical weapons stockpile under international control.

Mr Kerry said he was hopeful a date would be set for peace talks to take place, but added that the US taking military action was still a possibility.

"We are committed to trying to work together, beginning with this initiative on the chemical weapons, in hopes that those efforts could pay off and bring peace and stability to a war-torn part of the world," he said

"Much ... will depend on the capacity to have success here in the next hours, days, on the subject of the chemical weapons."

Mr Obama said he hoped the talks prove successful but added that he will insist any deal is "verifiable and enforceable".

Speaking after a meeting at the Oval Office of the White House with Kuwait's emir, Sheikh Sabah al-Ahmad al-Jaber al-Sabah, Mr Obama said: "I shared with the emir my hope that the negotiations that are currently taking place between secretary of state Kerry and foreign minister Lavrov in Geneva bear fruit.

"But I repeated what I've said publicly, which is any agreement needs to be verifiable and enforceable.

"Our two countries are in agreement that the use of chemical weapons that we saw in Syria was a criminal act, and that it is absolutely important that the international community respond in not only deterring repeated use of chemical weapons, but hopefully getting those chemical weapons outside of Syria."

Russia hopeful a 'Geneva 2' may pave the way for peace talks

After meeting UN envoy Lakhdar Brahimi, Mr Lavrov and Mr Kerry said they hoped to meet in New York in about two weeks, around September 28 during the UN General Assembly, to see if they could schedule a new international peace conference on Syria.

Mr Lavrov, voicing regret at the failure of an international accord reached in Geneva last year, said he hoped a "Geneva 2" meeting could lead to a political settlement for Syria.

"We agreed ... to see where we are and see what the Syrian parties think about it and do about it," he said.

Russia, which has resisted calls from Syrian rebels and Western and Arab leaders for Mr Assad to make way for a transitional government, said Mr Lavrov and Mr Kerry had agreed that only a political solution could end the violence.

We are committed to trying to work together, beginning with this initiative on the chemical weapons, in hopes that those efforts could pay off and bring peace and stability to a war-torn part of the world.

US Secretary of State John Kerry

Mr Assad's Syrian opponents, many of them disheartened by Mr Obama's failure to make good on threats to launch military strikes, say they see no place for the Syrian president after the war.

However, neither side has been able to finish the fighting, leaving the country's territory divided and its people in misery, including two million who are now refugees abroad.

The Syrian opposition coalition, which has struggled to form a coherent response to the Russian proposal, said it would appoint a provisional prime minister on Saturday to raise its international credibility.

National Coalition member Khaled Khoja says the opposition is still willing to enter into talks with the Assad government if the balance of military power is redressed.

"We are not against Geneva 2, but not under these conditions. The balance of power is not right now. What would restore it is either an air strike or weapons for the Free Syrian Army," Mr Khoja said, referring to more sophisticated anti-tank and anti-aircraft weapons that rebel brigades generally lack.

US, France and Britain to meet on Monday

It has also been confirmed that following talks with Mr Lavrov, Mr Kerry will meet with French and British foreign ministers for talks on Monday.

Mr Kerry, French foreign minister Laurent Fabius - who cancelled a visit to Mongolia for the talks - and British foreign secretary William Hague will attend the working lunch.

State Department spokeswoman Jen Psaki confirmed the information from the French foreign ministry, before adding that Mr Kerry would also meet with Saudi foreign minister Saud al-Faisal.